Bone Plate

ABSTRACT

The aim of the invention is to enlarge the possibilities of use of conventional bone plates and increase their flexibility of manipulation. To this end, the invention proposes a bone plate comprising a bottom side that is to rest against the bone and an upper side opposite to the bone as well as a plurality of holes located preferably along the longitudinal axis of the plate, through which bone screws can be inserted to be anchored to a bone. At least one of these holes is a continuous oblong hole comprising a longitudinal axis running in the direction of the longitudinal axis of the plate. A retaining structure, such as thread flights, is provided in a partial area of the lateral side of the oblong hole, said thread flights, when see in a direction transversal to the plane of the upper side, are arranged only over a part of the depth of the oblong hole. In the direction transversal to the plane of the upper side, above and/or below the thread flights, a support structure with smooth walls for the positive fit with a correspondingly configured negative structure at a screw head or screw neck of a bone screw is provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of co-pending applicationSer. No. 11/817,651, which is a national stage of and claims the benefitof priority of International Patent Application No. PCT/EP2006/010985,filed on Nov. 16, 2006, which claims priority to European PatentApplication No. 05028290.4, filed Dec. 23, 2005, and European PatentApplication No. 06010835.4, filed May 26, 2006, all of which are reliedon and incorporated herein by reference.

BACKGROUND OF THE INVENTION

The invention concerns a bone plate.

Bone plates are known, for example, from CH 462375, WO 2000/53111, WO2001/54601 or EP 0760632 B1.

The configuration of the holes in this prior art is such that theyconsist of a combination of two intersecting holes with differentdiameters and are combined into a continuous hole, and each side of thecontinuous hole with its fixed diameter has its own functionality andalso needs to be considered separate from each other.

Thus, for example, it is not possible to use a standard cortical screwat the thread side of the continuous hole, but instead only a screw withheaded thread.

The other side of the continuous hole, not having a threaded part, isonly suitable for insertion of a standard cortical screw, which can alsobe applied with compression and angle variability.

Thus, one could also separate the holes entirely from each other, sincethey have no functional interfaces.

This drawback then runs as well throughout the entire application, forwhen inserting a standard cortical screw one must also make sure that itis located on the proper side of the continuous hole.

From U.S. 2004/0087951 there is known a bone screw having a threadedsegment and smooth-wall segments arranged one on top of the other on itsscrew head, looking in the direction of the longitudinal axis of thescrew. These smooth-wall segments serve for a flexible receiving of thescrew in corresponding guideways.

BRIEF SUMMARY OF THE INVENTION

Based on the above, the problem of the invention is to improve the usagepossibilities of a bone plate and enhance its flexibility ofmanipulation.

This problem is solved by one embodiment of a bone plate comprising abottom side that is to rest against the bone and an upper side oppositeto the bone as well as a plurality of holes located preferably along thelongitudinal axis of the plate, through which bone screws can beinserted to be anchored to a bone, wherein at least one of these holesis a continuous oblong hole comprising a longitudinal axis running inthe direction of the longitudinal axis of the plate, wherein threadflights are provided in a partial area of the lateral side of the oblonghole, said thread flights, when seen in a direction transversal to theplane of the upper side, are arranged only over a part of the depth ofthe oblong hole, characterized in that, in the direction transversal tothe plane of the upper side, above and/or below the thread flights, asupport structure with smooth walls for the positive fit with acorrespondingly configured negative structure at a screw head or screwneck of a bone screw is provided. Advantageous modifications areindicated in further embodiments. Finally, in another embodiment, asystem is indicated, comprising of a bone plate according to theinvention and at least one bone screw suitable for it, which can beregarded as a fixation system on the whole.

The essence of the invention for the new bone plate is that both athread and a smooth-wall support structure are arranged in a partialsegment, uniformly one on top of the other, looking in a directiontransverse to the plane of its upper side. Thanks to the interplay ofthread and smooth-wall support structure, a bone screw withcorrespondingly configured negative structures can be held in the boneplate especially effectively, locked in position and protected againsttilting. Thanks to the interplay of the thread in the oblong hole with acorrespondingly fashioned counterthread on the head or neck of the bonescrew, the bone screw is pressed firmly into the support structure witha negative structure or bearing structure corresponding in shape to thesupport structure and thus fixed securely.

In one preferred embodiment, the thread flights in the bone plate of theinvention extend along a shorter segment of the oblong hole than thesmooth-wall support structure. This technical measure allows inpractical use an easy and secure sliding of a bone screw provided with athread at its neck and/or head and with the negative structure into thestructures (thread, support structure) arranged at the oblong hole witha continuous movement of the bone screw along the oblong hole. A slidingtransition to a smooth-wall support structure is easier to realize thana sideways sliding into a thread. Thus, the guiding for a secure andaccurate transition of the thread at the head and/or neck of the bonescrew can be accomplished by the initially occurring interaction betweensupport structure and negative structure, dictating the direction.

Preferred angle ranges for the wrap of the thread arranged on the headand/or neck of the bone screw and engaging with the thread of the oblonghole are 60°≦α≦190°, preferably 60°≦α≦180°, and for the correspondingwrap of the negative structure, 185°≦β≦300°. These values were bestsuited in tests for a preferably continuous movement of the screw alongthe oblong hole, while still ensuring firm support for a bone screwsecured in the thread/support structure of the oblong hole. A freemobility of a bone screw along the longitudinal axis of the oblong holemakes it possible to use this both to apply a pressing force directedonto the point of fracture and to lock the plate angle-fixed.

Especially in a preferred modification the thread looking in the planeof the upper surface engages at most 180 degrees of a circularcircumference of a screw head or neck of a bone screw, to be broughtinto engagement with the latter. This configuration has the effect thata bone screw can move freely along the longitudinal axis of the oblonghole, and thus it can be used both to apply a pressing force directedonto the point of fracture and to lock the plate angle-fixed.

At present, a conical surface is preferred as the support structure. Insuch a structure, a correspondingly conically shaped surface (negativestructure) of the head or neck of the bone screw can be secured. Intheory, it is also possible to use other shapes for the surfaces of thesupport structures, for example, hemispherical surfaces.

It basically makes no difference to the bone plate of the inventionwhether the supporting structure is arranged first, seen from the upperside of the plate, and the thread is arranged in the lower region of thebone plate, or vice versa. One just as well have several thread segmentsin the bone plate, each of them alternating with and interrupted by atleast one segment with a support structure. Preferred is a sampleembodiment in which the threaded segment lies near the upper side of thebone plate and a support structure lies near the lower side of the boneplate.

A recess in the transitional region between thread and support structurefacilitates the passage of the screw head or neck, more precisely, theregion provided with the thread, into the segment of the oblong holeprovided with the thread, especially when pushing the bone screw alongthe oblong hole.

In one embodiment, the oblong hole has a first guide structure at theupper side of the bone plate. This serves to guide the head or neck of abone screw. This guide structure can be, for example, a circumferentialmargin with cross section in the form of a semicircle, in which acorrespondingly spherical or hemispherical negative structure on thehead or neck of a bone screw can slide. The guide structure defines aguideway. This guideway is a path, lying preferably in a plane, alongwhich an imaginary point on the screw head slides when the screw isshoved along the guide structure. Moreover, this guideway is intersectedby a longitudinal axis of the thread, which in the sense of theinvention is the axis about which a counterthread rotates when beingscrewed into the thread, at an angle different from 90 degrees. Thiskind of tilting between thread and guide plane has the effect that, evenfor a maximum wrap of 180 degrees situated in the plane of the surface,the thread or the support structure provides a rather firm support tothe screw head or neck, since the tilting leads to an effectivelygreater wrap, at least in a partial region of the thread. This effect isachieved by a “clamping” or “wedging” effect, produced by the tilting.

Furthermore, it is preferable that the guideway be inclined by an anglebetween 0 and 90 degrees relative to the plane of the plate. Here,moreover, an embodiment is preferred in which the thread and the supportstructure are arranged in a segment of the oblong hole in which theguide plane lies deepest, i.e., furthest away from the upper side of thebone plate.

The segment of the oblong hole provided with thread and supportstructure, according to the invention, is limited to a partial segmentof the oblong hole, which lies preferably on a narrow side of the oblonghole.

Advantageously, the oblong hole of the invented bone plate has a secondguide structure, besides the first guide structure described above,serving to guide bone screws with threadless head and neck (standardcortical screws). This separation of the guide structures allows for amore clean separation in the action of the two bone screws which canpossibly be employed with the invented bone plate.

By oblong hole in the sense of this invention is meant not only a holepattern produced by displacing a circle along a linear axis, butbasically any shape of an opening which is longer in a first dimensionaldirection than in a second dimensional direction. Thus, an oblong holein the sense of the invention can also have a “triangularly tapering”,oval, or “keyhole-shaped” configuration. Preferably, this oblong hole iscontinuous, i.e., with no “barriers” protruding into the hole.

Finally, the invention specifies a system comprising of a bone plate asdescribed above and a bone screw. The bone screw of this system has,according to the invention, a screw head or screw neck, on which it hasa thread structure and a bearing structure configured complementary tothe support structure of the oblong hole, being arranged one on top ofthe other and matching up with the corresponding negative structures inthe bone plate.

The bone plate can be stable-angle fixed and tightened at the same timewith a bone screw, configured specially with a thread and a negativestructure on the screw head and/or neck. However, it should beemphasized here that the bone plate of the invention can also be fixedwith standard bone screws or bone screws derived from such standard bonescrews, in particular, ones having neither a thread nor a negativestructure at their screw head or neck.

The bone plate of the invention—also together with the invented bonescrew—offers a great variety of possible applications, which makes itsuited for the fixation of the most diverse fractures.

For this, it is especially preferred that all openings in the bone platebe configured as oblong holes with the properties of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional benefits and features of the invention will emerge from thefollowing description of a sample embodiment by means of the encloseddrawings. These show:

FIG. 1, a first sample embodiment of the invented bone plate in athree-dimensional view,

FIG. 2, the bone plate of FIG. 1 in a view from above,

FIG. 3, the bottom side of the bone plate from FIG. 1, in an enlargedcutout,

FIG. 4, the bottom side of an alternative embodiment of the inventedbone plate, in an enlarged view,

FIG. 5, a cross section through a bone plate from FIG. 1 along itscentral longitudinal plane,

FIG. 6, a cross section according to FIG. 5, in enlarged view, with onlyone oblong hole depicted,

FIG. 7, a view as in FIG. 6 with the course of the guide structure drawnfor clarity,

FIG. 8, a sample embodiment of a bone plate according to the invention,in a top view,

FIG. 9, in an enlarged cutout, the top view of an oblong hole of asample embodiment of the invented bone plate,

FIG. 10, in an enlarged view, a longitudinal section through the oblonghole of FIG. 2,

FIG. 11( a) a front view of a bone screw with thread and negativestructure formed on its screw head to interact with the thread and thesupport structure in the invented bone plate, and FIG. 11( b) a frontview of a standard bone screw,

FIG. 12( a) a front view, comparable to FIG. 4, of a bone screw forinterworking with the thread and the support structure in the inventedbone plate and FIG. 12( b) a front view of a standard bone screw in onepossible position in the oblong hole for fixation of the bone plate,

FIGS. 13( a), (b) and (c) provide a sequence consisting of threeindividual views to illustrate the sliding of the bone screw, providedwith thread and negative structure on its screw head, into the segmentof the oblong hole with thread and support structure,

FIGS. 14( a) and 14(b) illustrate a sequence in two individual views,similar to FIG. 6, to illustrate the sliding of a standard bone screwinto the segment of the oblong hole with thread and support structure,

FIG. 15, the firm seating of a bone screw provided with thread andnegative structure in the thread and the support structure of the oblonghole in a section view transverse to the lengthwise dimension of thebone plate,

FIG. 16( a), FIG. 16( b), and FIG. 16( c) illustrate three differentpossible additional shapes of an oblong hole of an invented bone plate.

FIG. 17, a front view of the invented bone plate with drill jig sleevemounted to drill a screw hole in a bone, and

FIG. 18, a front view similar to FIG. 14, but with an alternativevariant of a drill jig sleeve.

The figures show schematically sample embodiments of a bone plateaccording to the invention and all of them are generally designated with1. The sample embodiments shown are in no way true to scale, but servemerely as a basic illustration.

DETAILED DESCRIPTION OF THE INVENTION

The invented bone plate 1 has an upper side and a lower side 3, servingto bear against the bone being fixated. Continuous openings in the formof oblong holes 4 are introduced into the bone plate between upper sideand lower side. The oblong holes 4 are continuous in these sampleembodiments, i.e., configured without any projections or similarobstructions reaching into the interior. The invented bone plate 1 haseight oblong holes 4 overall in these sample embodiments, yet withoutbeing limited to this number. The oblong holes 4 are configured asnarrowing toward one of the lengthwise sides in the preferred sampleembodiments. However, as is shown for example in an alternativeembodiment per FIG. 4, they can also have a straight course andcorrespond to the shape produced by displacing a circle along apredetermined distance. Of course, all other conceivable shapes ofoblong holes are also possible, as long as they are continuous in form,i.e., free of obstruction in their interior. Corresponding examples arepresented in FIGS. 16 a) to c).

At one end face of each oblong hole are formed a thread or threadflights 5, as well as a support structure 6. The thread 5 and thesupport structure 6 lie one above the other in a direction transverselyto the plane of the plate, while in these sample embodiments the thread5 is arrange on top (toward the upper side 2 of the bone plate 1) andthe support structure 6 underneath (toward the lower side 3 of the boneplate 1). In the transitional region between thread 5 and supportstructure 6, a recess 7 can be introduced (see FIG. 6). However, thisrecess is not absolutely essential, and it is not present in the variantembodiments shown in FIGS. 8 through 13, for example. The supportstructure 6 is formed by a smooth-walled segment of the oblong hole,being hemispherical in the sample embodiment shown in FIGS. 1 to 7, orconical in the sample embodiment shown in FIGS. 8 to 13.

As is especially evident in FIGS. 1, 2, 3, 8, 9 and 16, the thread 5 andsupport structures 6 of the oblong holes 4 in the sample embodimentsshown there are arranged at the narrow sides of the latter, usually atthe tapered narrow sides, being oriented in the direction of the middleof the plate. The longer lengthwise axes of the oblong holes 4 run alonga lengthwise axis of the plate.

The oblong hole 4 contains a circumferential guide structure 8 at itsopening facing the upper side 2 of the bone plate 1. This is formed by amargin with semicircular cross section, which is introduced in theoblong hole 4, for example, by a chip-removal machining step (such asmilling). As an illustration of this, FIG. 7 shows a “bathtub” shapedtrend of this margin, i.e., the guide structure 8. One also notices herethat the guide structure 8 is inclined at an angle δ to the course ofthe plane of the plate Eρ, dictated by the trend of the upper side 2 ofthe bone plate 1. Likewise, the guideway or guide plane E_(L) is alsoinclined relative to a lengthwise axis A_(G) of the thread, and this byan angle 6.

In particular, it is evident from FIG. 9 that the thread flights 5 inthe sample embodiments shown in FIGS. 8 to 10 and also 16 run in ashorter circumferential segment of the oblong hole 4 than the supportstructure 6. While the former extend over an angle α of preferablybetween 60 and 190 degrees, the latter extends over an angle range β ofpreferably between 185 and 300 degrees. This choice of different wrapregions allows for a smooth sliding of the bone screw into this regionwith a reliable fixation at the end, as shall be further explainedbelow.

FIGS. 11 a) and 11 b) show a bone screw 11 with a screw head 12specially designed for interworking with the invented bone plate 1 and astandard bone screw 9 with a screw head 10 shaped smooth and sphericalat the bottom side. The screw head 12 contains at an upper segment athread 13 which is spherically configured in this sample embodiment and,underneath this, looking in the direction of the lengthwise axis of thescrew, a segment with a bearing or negative structure 14. This bearingstructure 14 is smooth walled in this sample embodiment with partlyspherical or conical trend, tapering in the direction of the screw tipand matched to the support structure 6 of the particular sampleembodiment, and it is complementary to the shape of the supportstructure 6 of the bone plate 1.

The oblong hole 4 in the sample embodiment shown in FIGS. 8 to 10contains two guide structures 8 and 8 a at its opening facing the upperside 2 of the bone plate 1. While the first guide structure 8 is a guidestructure for the guiding of a bone screw 11 with thread 13 and bearingstructure 14 at the screw head 12, the guide structure 8 a serves toguide the screw head 10 of a standard bone screw 9. The two guidestructures 8, 8 a are arranged one on top of the other, formed by amargin with semicircular cross section, which is made in the oblong hole4, for example, by a chip-removal machining step (such as milling). Thetwo guide structures 8, 8 a each define a guideway, running at aninclination to the surface of the bone plate 1. In particular, the firstguide structure 8 (or the guideway defined by it), as in the previouslydescribed sample embodiment, intersects the plane of the plate,determined by the trend of the upper side 2 of the bone plate 1, at afirst angle other than 0 and 90 degrees. Likewise, the guideway is alsoinclined relative to a lengthwise axis of the thread, and this likewiseat an angle other than 0 and 90 degrees.

FIGS. 12 a) to 14 show the interworking between a bone screw 9 of thetraditional kind and a bone screw 11 of the adapted kind in theinvention and the bone plate 1 of the invention. Thus, the functioningof the bone plate 1 of the invention and its elements shall now also beexplained by means of these figures.

FIG. 12 b) and 14 show a traditional bone screw 9 inserted into theoblong hole 4 of the bone plate 1, in two different positions. This bonescrew 9 lies with the smooth, spherically formed underside of the screwhead 10 against the complementary formed guide structure 8 (in the firstsample embodiment) or 8 a (in the second sample embodiment) of theoblong hole 4 and can thus be shoved along the lengthwise axis of theoblong hole 4, following the guideway dictated by this guide structure.Due to the slanted position of the guideway, a compression effect isachieved when screwing in the bone screw 9, such that the bone plate 1is pressed in a direction or a bone being fixed therewith is pulled inthe other direction. In particular, the outer contour of the threadsegment formed by the thread flights 5 in the oblong hole 4 is formedsuch that it also forms a guide surface shaped complementary to theconically shaped underside of the screw head 10. This outer contour thusforms part of the guide structure 8 and 8 a. At this guide surface, thetraditional bone screw 9 can become tilted relative to the vertical(corresponding to the direction of the thread axis). This gives amultitude of possibilities for securing the bone screw 9 in the bone.This tilting is possible not only in a direction along the lengthwiseaxis of the oblong hole, but also in directions transverse to it, sothat ultimately one has a region of basically 360 degrees in which thescrew can be tilted relative to the thread axis.

Such a traditional bone screw 9 can be used with the bone plate 1 of theinvention to achieve a compression effect. However, this bone screw isnot suitable to achieving an angle-stable securing in bone plate 1 andbone. For this, one can use the bone screw 11 adapted to the bone plateaccording to the invention, as shall now be described with the help ofFIGS. 12 a) and 13 to 14.

The segment of the screw head 12 provided with the thread 13 has anouter contour (an envelope of the thread flights), which is likewisespherical and complementary to the contour of the guide structure 8. Inthis way, the bone screw 11 can be led into the guide structure 8. Thus,the bone screw 11 can also be used initially to accomplish a compressioneffect. But the peculiarity of the bone screw 11 is that it can besecured in stable position in the oblong hole 4 of the bone plate 1.This situation is shown, e.g., in FIG. 5 a). In this position, thethread 13 of the screw head 12 engages with the thread flights 5 in theoblong hole 4, and the bearing structure (negative structure) 14 lieswith positive fit against the support structure 6. Thanks to theinterworking of the thread flights 5 with the thread 13, the bearingstructure 14 is pressed firmly against the support structure 6, while itshould be noted that the support structure 6 and the thread flights 5are coaxially configured, just like the thread 13 and the bearingstructure 14 on the screw head 12. The transition from the screw head12, more precisely, the thread 13 on the screw head 12, to the threadflights 5 in the oblong hole 4 is facilitated and guided by theinitially occurring contact between the negative structure 14 and thesupport structure 6, which contact dictates a definitely guidedmovement. Thus, the start of the thread flight of the thread 13 can betaken securely into the thread flights 5, so that the thread 13ultimately engages with the thread flights 5, without tilting.

In a position as shown by FIG. 12 a), the thread flights 5 enclose thescrew head 12 and the thread 13, looking in a plane of the surface 2 ofthe bone plate 1, preferably by not more than 180 degrees. The screw 11is held in its position by a clamping effect, achieved by the tilting ofthe guideway dictated by the guide structure 8 relative to thelengthwise axis of the thread, and by the interworking of the supportstructure 6 (continuing to enclose it in the second sample embodiment ofthe bone plate 1) with the negative structure 14, while the negativestructure 14 is pressed axially into the support structure 6 by theinterworking of thread flights 5 and thread 13.

Only thanks to this fact is it possible to configure the oblong hole 4as continuous and serviceably over its full length for eithercompression or for angle-stable fixation.

FIGS. 17 and 18 show how the sleeves of drill jigs are connected to thebone plate for the operation to install the bone plate. The situationshown in FIG. 17 shows a simple drill sleeve 15, which is screwed by aspherical thread 16 and bearing structure formed at its lower end(corresponding to the structures on the screw head 12 of the bone screw11) into the thread 5 and the support structure 6 on the inside of theoblong hole 4. The drill sleeve 15 affords a drilling channel 17 on itsinside, which thanks to the proper fitting of the thread 16 and thebearing structure of the drilling sleeve 15 runs along the axis AG. Thedrilling sleeve 15 serves as an aid when drilling a hole in the bonebeing provided with the bone plate 1 to make sure that the drilled holeis perpendicular to the bone plate 1 and therefore a bone screw 11 canbe screwed into the bone with stable angle, so that its screw head 12with the thread 13 and the bearing structure 14 easily engages in thethread 5 and the support structure 15.

FIG. 18 shows a variant, in which an additional drilling sleeve 18 isplaced onto a drilling sleeve 18 so that the drilling channel 19 of thisdrilling sleeve 18 lies exactly parallel to the axis A_(G). With thisdrilling sleeve 18, one can drill screw holes in the bone, permittingthe above-described dual function of a bone screw 11. The bone screw 11is screwed into the bone at such a perpendicular angle as allows it toslide initially along the inclined plane E_(L) of the guide structure 8for a compression and then to engage by the thread 13 and the bearingstructure 14 on its screw head 12 securely and without tilting in thethread 5 and the support structure 6 on the inside of the oblong hole 4,so as to become fixed in its angle at the end of the process. Thus, thisenables a simultaneous compression and angle fixation in a single stepwith only a single screw.

The drilling sleeves shown are purely for example, and there are variousways of achieving the same results with drilling sleeves of differentdesign.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principals and applications of thepresent invention. Accordingly, while the invention has been describedwith reference to the structures and processes disclosed, it is notconfined to the details set forth, but is intended to cover suchmodifications or changes as may fall within the scope of the followingclaims.

LIST OF REFERENCE NUMBERS

1 bone plate

2 upper side

3 lower side

4 oblong hole

5 thread/thread flights

6 support structure

7 recess

8 guide structure

8 a guide structure

9 bone screw

10 screw head

11 bone screw

12 screw head

13 thread

14 negative structure/bearing structure

15 drill jig sleeve

16 thread

17 drill channel

18 drill jig sleeve

19 drill channel

A_(G) lengthwise axis of thread

E_(L) guide plane/guideway

Eρ plane of the plate

α angle

β angle

δ angle

1. A system comprising: a bone plate and at least one bone screw, saidbone screw comprising a screw head; said bone plate comprising: a bottomside for resting against a bone; an upper side opposite the bottom side;and a plurality of holes located along a longitudinal axis of the platefor inserting one or more bone screws to be anchored to a bone, whereinat least one hole is an oblong hole including a longitudinal axisrunning in the direction of the longitudinal axis of the plate; saidoblong hole comprising a guide structure defining a guideway which is apath along which an imaginary point of the screw head slides along saidlong hole when the screw is shoved along said guide structure; and aretaining structure for engaging the threads of said bone screw toarchive an angle-stable fixation of said bone screw in said oblong hole.2. A system according to claim 1, wherein said bone plate comprises asupport structure with smooth walls configured for the positive fit witha correspondingly configured negative structure at a screw head or screwneck of said bone screw is provided above or below the retainingstructure in the direction transversal to the plane of the upper sideand wherein the retraining structure extends along a shorter contoursegment of the oblong hole than the smooth-wall support structure.
 3. Asystem according to claim 2, wherein the smooth-wall support structurelooking in the plane of the surface is configured to enclose an angularregion (β) of a circular contour of the screw head or a neck of a bonescrew to be brought into engagement with the support structure, andwherein 185°≦β≦300°.
 4. A system according to claim 1, wherein theretaining structure looking in the plane of the surface is configured toenclose an angular region α of a circular contour of a screw head orneck of a bone screw, to be brought into engagement with this, andwherein 60°≦α≦190°.
 5. A system according to claim 1, wherein thesupport structure is a conical surface.
 6. A system according to claim1, wherein the support structure is a hemispherical surface.
 7. A systemaccording to claim 1, wherein the retaining structure is arranged in asegment located near the upper side of the bone plate, the supportstructure in a segment arranged near the lower side.
 8. A systemaccording to claim 1, wherein a recess is provided in a transitionalregion between retaining structure and support structure.
 9. A systemaccording to claim 1, wherein the oblong hole has, on the upper side ofthe bone plate, a first guide structure for guiding the head or neck ofa bone screw provided with screw bead and a negative structure on itshead or neck, and wherein the first guide structure defines a guideway(E_(L)) that is intersected by a longitudinal axis (A_(G)) of theretaining structure, at an angle (δ) other than 90 degrees.
 10. A systemaccording to claim 9, wherein the guideway (E_(L)) is inclined relativeto the plane of the plate (E_(ρ)) by an angle (γ) larger than 0 andsmaller than 90 degrees.
 11. A system according to claim 10, wherein theretaining structure is arranged on a narrow side of the oblong hole,preferably symmetrically to its longer axis, and in this region of theoblong hole the guide structure has the greatest distance from the upperside of the bone plate.
 12. A system according to claim 2, wherein theoblong hole has a second guide structure configured to guide bone screwswith threadless head and neck, and wherein the second guide structurehas a trend inclined relative to the surface of the plate and a segmentof the second guide structure situated nearest the lower side of thebone plate is in the region of the oblong hole in which the retainingstructure and the support structure are arranged.